Actually the OB CVX16 wasn't called an SS until it was brought back in '82. They didn't bring back the I/O version.
However, until the CVX series was discontinued due to the release of the metric series, with the 16' models the "SS" designation always meant it was an I/O.
The CVX18 was only built with an I/O hence the lack of "SS". When I had my '83 I always thought it was weird that it said "SS" on the bow and I have no clue why they did that. Of course I don't know why they brought back a discontinued boat versus trying to fix what was wrong w/Metric series. IMHO they were a definite step forward.